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Steel-Concrete Composite Floor Systems Subject to Fire – Phase 2

42ftCompositeFloorSpecimen_FireTest
Video snapshot of compartment fire experiment with a 12.8 m long composite steel-concrete floor specimen. 

NIST is conducting a multi-year research project to study the thermal and structural behavior of real-scale composite floor systems in fire. In Phase 1, five 12.8 m span specimens were designed in accordance with U.S. design codes and standards. One specimen was tested at ambient temperature to measure the flexural moment capacity and failure mode of the specimen. The other four specimens were loaded to 45 % of the ambient-temperature bending moment capacity and subjected to a maximum 4 megawatt compartment fire using natural gas fuel delivery system. Each composite beam specimen consisted of a W18 × 35 steel beam and a 1.83-m wide concrete slab cast on top of a fluted steel decking. The lightweight aggregate concrete slab was lightly reinforced for temperature and shrinkage control. Two types of shear connections were considered: (a) bolted/welded double-angle connections and (b) single-plate shear connections. The effects of slab continuity on the fire performance of the composite specimens were also experimentally evaluated.

In Phase 2, the test structure is a two-story, two bays by three bays gravity frame with each story height of 3.3 m. The test bay (at the center of the building) measures 6.1 m by 9.1 m and will be hydraulically loaded to service gravity loads. The fire will be produced by natural gas fueled burners with a total maximum capacity of 16 megawatts and confined to the test bay using enclosure walls. Columns will be protected against fire exposure. The first test will be a standard fire test to generate baseline data for current U.S. practice. For later test series, a test fire designed using NIST’s Fire Dynamics Simulator (FDS) will be used to simulate a post-flashover fire followed by cool-down. The measurements will include the fire heat release rates, gas temperatures, and heat fluxes, as well as displacements, forces, strains and temperatures in the composite floor systems.

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Created August 15, 2018, Updated December 6, 2019